Border police in southern Helmand province arrested the girl's father and were searching for the brother, named Zahir, who had escaped with the suicide vest, a commander said.
"The guy named Zahir had the suicide vest and escaped, but she was still there and when our commander of the battalion heard her voice, they surrounded the area and brought this girl to their base, and we all heard her story on how she was forced into this action," Col Hamidullah Sediqi Sediqi said.
"I said I won't go, then he took off the vest and tried to convince me that they (police) will die and I will remain alive," Spozhmai said.
Afghanistan's Interior Ministry announced the girl's detention in a statement Monday, saying she was 10 years old and describing her brother as a "Taliban commander." But Taliban spokesman Qari Yousef Ahamdi denied any involvement in the case.
Afghan president Hamid Karzai condemned the action, calling it "un-Islamic.